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Purifiers. Filters, & Cleaners

The Technology of Air Purifiers

There are a large number of technologies that are used to address the need for clean indoor air.  There are only a few however that are actually effective in treating the air without harming the individual.  These are HEPA, Electrostatic, UV, Activated Carbon, and some other adsorption materials like Zeolite Clay.  We have written several articles about these technologies and they are included here:

  • HEPA - probably the best known and most effective for air purifiers.  These are also found in cleanrooms and other industrial applications.
  • Activated Carbon - used initially to filter water this is a great media for absorbing chemical pollutants.
  • Electronic - an overview and background about this technology.
  • UV - ultraviolet light kills microorganisms such as viruses and bacteria. How do UV Air Purifiers work?
  • Ionic Breeze - This is a technology shown not to work.
  • Ozone - This technology works well in industrial applications but is dangerous to humans.
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There are many different technologies and mediums that are used in air purifiers so they can deliver clean and safe air to users. The different types of technologies that are used include HEPA, electronic, UV, ionic breeze and chemical adsorption mediums. Some of the technologies used are proven to be more effective than others and some may be harmful to users. Each type of technology that is used in an air purifier is designed to clean the air of specific particles and odors. The effectiveness and efficiency of each technology is measured in different ways. Choosing the best air purifier with the most efficient technology can be easy with some research and comparison.

High Efficiency Particulate Air filter, or HEPA, technology is one of the most popular technologies used in air purifiers. An air purifier that is equipped with a HEPA filter is able to absorb 99.7% of all particles that are 0.03 microns and larger in size. Most harmful particles that are found in the air are measured to be about 0.03 microns or larger. The HEPA filter is able to absorb most particles and make the air fresher and cleaner to breathe in. Chemical fumes, bacteria, dust particles and pollen are absorbed by the filter and the air that is produced by the air purifier after being filtered is free of these contaminants. Once the air enters the air purifier and flows through the HEPA filter, it is released into the room to circulate. 99.7% of all particles that were in the air and passed through the filter that were 0.00001182 inches and smaller in size were absorbed. HEPA technology has been around since the 1940's and is still being improved upon and advanced. Many air purifiers are so efficient due to the use of these filters.

Another type of technology that can be found is electronic technology. Air purifiers that use electronic technology are very effective in cleaning the air of particles, dust and fumes. Electronic technology uses an electronic charge to attract particles to collection plates and eliminates them from the air. Electronic air purifiers are proven to be 95% efficient and can absorb most particles from the air. Electronic air purifiers can be compared to magnets. They use static electricity to charge particles in the air. The opposite charge can be found in the air purifier and the two charges are attracted to each other, trapping the particles inside the air purifier. Electronic air purifiers are low maintenance and only require cleaning of the collection plates for optimal efficiency. The effectiveness of electronic air purifiers has become apparent due to the high percentage of efficiency.

Ionic breeze air purifiers are a technology used whose efficiency is yet to be proven. The ionic breeze air purifier is supposed to catch the particles on metal blades inside the purifier that carry an electric charge. The blades move the air through the unit by causing a flow of air. The negative ions and positive ions are supposed to attract and make the particles and fumes in the air stick to the blades. However, the ionic breeze purifiers are found to only be able to absorb about 30% of the particles in the air. The air purifier that used ionic breeze technology was also found to not take in all the air in an enclosed room. It was measured to have left about 5% of the contaminated air in the room to circulate without it ever being absorbed by the purifier. Consumer Reports gave ionic breeze purifiers a “poor” rating. Although they are readily available, consumers who research air purifying technologies before making a purchase are sure to avoid ionic breeze air purifiers.

One type of medium that is added to some air purifiers in order to eliminate odors or certain types of fumes is called chemical adsorption technology. Chemicals such as activated carbon, Zeolite or potassium permanganate are added to some air purifiers. They are able to add more efficiency to the filtering system that is used in the air purifier. These chemicals can work to absorb smoke or chemicals that may be present in the air. They specialize in neutralizing odors and absorbing chemicals. An effective filtering system that is also equipped with chemical adsorption materials can produce cleaner and fresher-smelling air.

There are many different types of technologies and mediums that are used in these air purifiers. Some of these technologies are more efficient and effective than others. The effectiveness of these technologies are measured and explained and can be found with a little research. When a consumer is choosing the most effective air purifier, the technology used in air purifiers is the most important factor he or she should consider.

HEPA Air Purifiers

High Efficiency Particulate Arresting (HEPA) filters have been around for quite some time.  In the 1950s the US Atomic Energy Commission needed something to remove small particulates that are radioactive. Since then HEPA air purifiers have been using this technology to clean the indoors in cleanrooms to beauty parlors. HEPA products are also one of the many techniques and products used by Allergy and Asthma doctors to help alleviate the symptoms of those conditions. First we will discuss what HEPA really is.

Imagine a filter that only allows very tiny particles to pass through. If we placed a single sheet of this HEPA paper in front of a fan constrained as it would be in air purifiers, very little air would be able to pass because of the small size of the holes. In addition, air purifiers made like this would need to have the filter changed often because the holes would plug rapidly. Now if we double the size of the sheet we would get twice the airflow and filter life. You can not keep growing the sheet larger because it would be impractical. Instead let us try folding the paper back and forth so that we can present a very large surface area to the airflow and thus the HEPA made this way would be efficient. This is how real-world HEPA filters are made in real HEPA systems. Some have as much as 40 square feet of the filter material folded into the HEPA section. As a side note the material from which HEPA is constructed is either fiber or paper-like on one hand or a polymer on the other.

HEPA material does not look like a screen or a colander. Instead it looks like a very thin bail of fibers.  Thus the air has to find a route through this maze of fibers.  There are three ways the HEPA filter stops particulates.  First and the easiest to understand is that a particle runs into a fiber and sticks. Secondly, the particle gets within one diameter of a fiber of the HEPA filter and while it tries to "skid by" the fiber it is gets stuck on the fiber.  Third, as a very small, about 0.1 micron, particle moves in the gas flow it dithers about due to collisions with molecules (Brownian motion)  and again happen to slide close to a fiber and get caught.

Therefore, HEPA air purifiers stop mold spores as well as many bacteria and viruses and of course larger items such as dust. Most air purifiers claim to be 99.97% efficient at removing particles 0.3 microns from the air that passes through the HEPA filter.  The operative phrase is "pass through"!  If the airflow does not have an opportunity to pass through the HEPA filter it will not be cleaned.  Therefore the claim of 99.97% of all .3 and larger particles being removed is not accurate in poorly designed HEPA air purifiers where some of the airflow may pass around the HEPA filter and return to the room not cleaned. The Austin Air HealthMate Plus series is the only line that specifies that over 95% of the airflow that enters the air purifier goes through the HEPA filter.

As good as that sounds pure HEPA air purifiers do not remove odors, chemicals or gasses. Since these are molecular level substances the 0.3 micron holes are large compared to the gas molecules. Therefore typical HEPA air purifiers have some level of activated carbon based material to absorb odors and chemicals. The activated carbon that is included with all of these units comes in a number of varieties.  This varies from a thin mat in an NeoAir unit, to pounds of activated carbon in an AllerAir Air Purifier.  In any form the carbon absorbs gasses that will not be caught by the HEPA element.  These chemicals are either harmful gasses or those that cause odors. 

HEPA air purifiers are straight forward, a fan forces airflow through a filter.  The more times the airflow goes through the filter in an hour the cleaner the room. So, the bigger the room, the bigger the product, or our preference, the more small air purifiers.  Why?  Think about a long narrow room.  If you put the product at one end how often is the air from the other end going to get through the HEPA filter?  Not often.  If you put smaller air purifiers at either end of the room the air will only have to move half as far to get through the HEPA and get clean.

Activated Carbon in Home and Room Air Purifiers

I. Introduction
The presence of activated carbon in room air purifiers may be a mystery to you, unless you're a aquarium hobbyist, or own a water purification system which uses carbon. For many people, the first time they encounter it is in selecting home air purifiers. Although most of our customers begin their search because of allergies or asthma, many soon realize how much odors and the chemicals with can cause them also contribute to their respiratory problems. That's why most quality room air purifier systems also address these issues.

II. History and Use in Purification Processes
As many as 2000 years ago, human beings were using activated carbon to remove impurities from water. Even then it's exceptional adsorption qualities were known. However, it was not until the early 1900's that it was produced in a form (as powder) that could be sold commercially. At that time it was used to purify water (so that it had no smell or taster) and to take the color out of sugar. As World War I got into swing it was discovered that it could be used in gas masks to protect soldiers, as well as for war time water and air purifiers. Instead of being used in powder form, granular activated carbon was developed. From that point on, activated carbon was used in many ways.

III. Why Is It Called "Activated"?
If you are unfamiliar with activated carbon and wonder why it is called "activated" and if there is such a thing as non-activated carbon, this will solve the mystery. The heat used in making carbon "activated" drives out impurities so there are places for impurities from your air to reside when it is used in an air purifier. After activated carbon is used for a while, it can actually be reactivated by cooking it again. However, this is impractical and dangerous. "Non-activated" carbon is soot or charcoal.

Activated carbon is described in a variety of ways, and there are a variety of types,  but generally it includes a wide range of amorphous carbon-based materials which exhibit a high degree of porosity and an extended surface area. In simple terms, this means that it has excellent absorbent characteristics that make it very useful for a wide variety of filtration processes including air and water.  

IV. How Is Activated Carbon Used in Home Air Purifiers?
In room air purifiers, the activated carbon is often combined with other minerals like zeolite.  Zeolite can absorb ions and molecules and thus act as a filter for odor control, toxin removal and as a chemical sieve. In some units, the carbon may be impregnated with a potassium iodide or blended with impregnated active alumina to increase the absorbent qualities. These home air purifiers are particularly helpful to people with Multiple Chemical Sensitivity (MCS), because they absorb formaldehyde which is found in carpet, wood paneling, and furniture upholstery. Perfumes as well as chemicals in household cleaning items are also removed, making the environment much more breathable for people in general, but especially asthma sufferers, babies, children, and the elderly.

V. The Carbon in Room Air Purifiers
The type and amount of activated carbon, other materials with which it is blended, and how it is used in home air purifiers depends on the brand and model. Here are the highlights:
Austin Air HM400 – contains 18 pounds of granular activated carbon impregnated with zeolite to enhance chemical adsorption.
Austin Air HM400 SuperBlend (also called Plus) – contains 18 pounds of granular activated carbon impregnated with a blend of zeolite and potassium to make it effective at removing formaldehyde.

VI. Summary - Home Air Purifiers
For many people, particulates such as pollens or pet dander are the main irritants, with odor and chemical adsorption being less important or not important at all. For others who need a high degree of both, it is best to look at the higher caliber room air purifiers which offer outstanding particle, odor and chemical removal. VOC's (volatile organic compounds), smog, ozone, fumes from cooking, pets, or tobacco can be unhealthy or irritating for anyone not just allergenics and asthmatics. If you're going to have home air purifiers anyway, it only makes sense to get some that can absorb practically everything.

Electronic Air Purifiers

The technology used in air purifiers can be diverse and unique. There are many different air purifier companies that use different types of technology and mediums to achieve the goal of clean air. Although there are different filtering systems used in air purifiers, many of the systems are just as efficient and effective. Each system has different qualities and specialties that make them exclusive and individualized. An electronic air purifier is an air purifier that uses an advanced and effective type of technology to absorb contaminants in the air. Electronic air purifier products are used for businesses and residences in order to keep the air indoors safer and healthier for people to breathe. The filtering system used in an electronic air purifier uses a cutting edge design and knowledge of the behavior of contaminants in the air in order to work powerfully.

Static electricity is the main source of technology used by electronic air purifiers in order to clean the air. The static that is developed by the machine is used to attach a charge to all particles in the air that is taken in by the air purifier. When the particles possess a charge, this charge is attracted to the opposite type of charge. This opposite charge is placed onto collection plates or other types of medium inside the air purifier. This medium attracts the charged particles and they stick to the charged medium instead of staying in the air. Electronic air purifiers are proven to be more efficient at absorbing particles. The reason electronic air purifiers are more effective at cleaning the air is that when particles are charged as opposed to just being absorbed, they stick easier to the medium. There are more particles removed and there is a better chance of them being absorbed by the filter when they possess the charge given by an electronic air purifier. An electronic air purifier is measured to have 95% efficiency or more. The size of collection plates, rate of air flowing through the air purifier and how much power is in the electric field are factors that can affect how much efficiency is mastered from the air purifier.

There are two different types of electronic air purifiers. Some electronic air purifiers use a one-stage system to clean the air while some use a two-stage system. The one-stage system in an electronic air purifier charges the particles and sticks them to the collection plates. There is only one step that the air goes through of filtering once it enters the air purifier. In a two-stage system, however, the air enters the air purifier and the particles in the air are charged using high-voltage wires. The charged particles are then pulled into metal plates that are charged oppositely. Both types of electronic air purifiers are just as effective at removing particles from the air.

Both types of electronic air-purifying systems also require very low maintenance. There are no filters to change and the air purifiers tend to stay relatively clean. If there is build up that develops, the collection plates can be wiped down with a damp cloth. All of the build up from particles will be removed by a simple wipe and the collection plates will be good as new and perfectly charged. If the collection plates are kept clean and free from particle build up, they will remain efficient and effective in cleaning the air.

Electronic air cleaners are able to remove particles, fumes, odors and gases from the air. The technology used in electronic air cleaners makes them one of the most effective and advanced types of air purifiers on the market today. Electronic air purifiers are an efficient and low maintenance type of air purifier. They are easy to care for and deliver the same quality as other filtering systems on the market. With at least 95% efficiency, it's no wonder that electronic air purifiers are becoming a popular and convenient way to provide clean and healthy air.

UV Air Purifiers

There are a number of manufacturers of air purifiers who have begun to include a UV stage in their products. This is done so that the air purifiers address the concerns of those who are concerned about microorganisms such as bacteria and viruses. The at-risk very old and very young are typically the population for which UV air purifiers are purchased. Therefore these air purifiers are often seen in nursing homes or day care centers.

Ultraviolet or UV light has a shorter wavelength than violet light which has the shortest wavelength in the visible spectrum. Thus UV is in visible to the human eye. The UV spectrum has been divided into three categories: 380–315 nm which is called UVA and was used in the “Backlights” of the 70s, 315–280 nm which is called UVB, and <280 nm which is called UVC and the range which kills microorganisms. UVA, UVB, and UVC can all cause damage to the eyes and also cause skin cancer.

UV is effective in killing organisms such as bacteria and viruses. It achieves this by disturbing the DNA of the organism at a molecular level. There are two wavelengths of UV light that are best absorbed and thus most effective at killing microorganisms. These are 185 nm and 265 nm. This means that for a UV lamp to be effective killing microorganisms it must emit energy in or around one of those wavelengths.

Keeping track of bulb life is critical. The bulbs will continue to “light” with the violet color which is a side effect of the bulb technology after they have stopped emitting in the UVC range. So when you start using your UV based air purifiers or put in new bulbs it is critical that you write the date in permanent marker on the bottom of the air purifier so that you will not forget. Then calculate the life of the bulbs based on the air purifiers manufacturer's recommendations and write the change date on you calendar.

While UV technology is excellent at destroying viruses and bacteria it should not be employed without a particulate filter system ahead of the lamps.  Without a particulate filter system too many microorganisms may be shaded from the light by particulates.  Therefore, most air purifiers that employ UV start by filtering the air with HEPA and and use the UV as a final stage of filtration.

How do UV Air Purifiers work?

Why are Sharper Image Ionic Breeze air purifiers so popular?

The Sharper Image Ionic Breeze seems to be ubiquitous – these ionic products are everywhere!  Ionic Breeze ads run on scores of channels, versions are sold in countless publications, and the products are sold in lots of stores, so it must be good right?

Well, not exactly.  The reason that the Ionic Breeze appear to be so popular is that its marketers are absolutely brilliant, and relentless!  The intensity of advertising these  purifiers gives it the appearance of popularity. And now there are competitors selling the same ionic technology with the same faults.

Here's what one of the independent product testing publication most recently had to say about the Ionic Breeze air purifiers: " it proved unimpressive" and that their tests "found almost no measurable reduction in airborne particles."  Sharper Image complained saying tests based on the industry standard for measuring clean-air delivery rate (CADR) were inadequate, and that Ionic breeze products are vastly different from the technology of other air purifier technology and would do better in a longer test. 

The publication re-examined its test procedures and had them reviewed by an independent expert. It then re-tested and reported that the Ionic air purifiers removed very little dust in a test lasting over 100 minutes.  They surmised that if it performed at that level for 100 minutes, it wouldn't become more effective, just by running it longer. Generally, it didn't come close to the performance of other air purifiers tested. 

How it works: The Ionic Breeze air purifiers use a charged plate electrostatic system. It works much like the Friedrich C90B except that it has no fan.  The Ionic Breeze is counting on the electrostatic plates to move the air though the air purifier.  To some extent it does move air as you can see with the wiggling ribbons on TV.  What they fail to mention is that it moves very little air.  The typical air purifier that we sell moves 200 to 400 cubic feet of air a minute.  If you put the little ribbons from the ionic breeze air purifier commercial on these they would be blown off.  To put this in perspective, 400 cubic feet is contained in a a room with 8 foot ceilings that is about 9 foot by 6 foot.  The "real" air purifiers move all of this air in ONE Minute.   The little wiggling ribbons probably move a couple of cubic feet per hour not enough to call the ionic air purifiers "real" air purifiers.

The Ionic Breeze probably does some good, and it is a nice design.  It's compact too. Plus the company typically offers freebies with your order and a good payment plan.  But if you have serious allergy or asthma problems, you are probably better off going with a less well advertised but more substantially performing air purifier.

UPDATE: On May 8, 2006 The Sharper Image introduced the Hybrid GP version of the ionic breeze.  This unit uses a fan and appears to have about a 125 CFM output.  This is very poor for a $400 unit.  The  Hybrid GP has a device that gets rid of almost all of the Ozone that is dangerous.  Would you buy an air purifier from a firm that has sold millions of non-fan, non-working units that produce Ozone to the American public?
 Ionic Breeze is a Registered trademark of the Sharper Image company. is not associated with the Ionic Breeze product or Sharper Image.

Answer the following questions:
  • Does the chosen manufacturer have independent tests to prove its claims?
  • How does the machine purify the air?
  • Does the chosen air purifier generate ozone? Is it safe?
  • How much will it cost to run? How much will it cost to replace filters and parts?
  • Is it noisy?
  • Is the technology clean and environmentally friendly?
  • How big and heavy is it?
  • Will it interfere in my house décor?
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